Disable TAA sharpening on alpha

com.unity.render-pipelines.high-definition/CHANGELOG.md

@@ -216,6 +216,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Updated Light's shadow layer name in Editor.
 - Increased path tracing max samples from 4K to 16K (case 1327729).
 - Film grain does not affect the alpha channel.
+- Disable TAA sharpening on alpha channel.
 
 ## [11.0.0] - 2020-10-21
 

com.unity.render-pipelines.high-definition/Runtime/PostProcessing/Shaders/TemporalAntialiasing.hlsl

@@ -11,7 +11,6 @@
     #define CTYPE_SWIZZLE xyz
 #endif
 
-
 #if UNITY_REVERSED_Z
     #define COMPARE_DEPTH(a, b) step(b, a)
 #else
@@ -49,6 +48,8 @@ float4 Fetch4Array(Texture2DArray tex, uint slot, float2 coords, float2 offset,
 // Options
 // ---------------------------------------------------
 
+#define SHARPEN_ALPHA 0 // switch to 1 if you want to enable TAA sharpenning on alpha channel
+
 // History sampling options
 #define BILINEAR 0
 #define BICUBIC_5TAP 1
@@ -717,5 +718,11 @@ CTYPE SharpenColor(NeighbourhoodSamples samples, CTYPE color, float sharpenStren
     linearC = linearC + (linearC - linearAvg) * sharpenStrength * 3;
     linearC = clamp(linearC, 0, CLAMP_MAX);
 #endif
-    return linearC * PerceptualWeight(linearC);
+    CTYPE outputSharpened = linearC * PerceptualWeight(linearC);
+
+#if (SHARPEN_ALPHA == 0 && defined(ENABLE_ALPHA))
+    outputSharpened.a = color.a;
+#endif
+
+    return outputSharpened;
 }